TRANSACTIONS OF THE SECTIONS. 87 



jnatter which is applied in the material we now use extensively for separating the 

 ammonia fi-oni coal-gas, with this improvement, that the acid instead of Deing in the 

 liquid state is solid, and is at once m the purifier converted into crystallized sul- 

 phate of ammonia. 



In saturating sidphuric acid with carbon it is not necessary to use the gaseous 

 hydrocarbons, as almost any vegetable matter will do; sawdust is used. The 

 material is prepared by heating together, at a temperature of about 280° Fahr., 

 equal weights of sulphuric acid, sp. gr. 1700, and sawdust. 



At that temperatiue the organic matter of the sawdust is broken up, and the 

 carbon eliminated solidifies the acid ; at the same time the acid dissolves as much 

 carbonaceous matter as it wUl take up. 



The author cannot say what is the organic compound dissolved by the acid, only 

 that in this form of satiiration the acid does not in the least injure the illuminating 

 power of the gases passed through it. 



On accoimt of the immense sm-face of acid exposed to the gas when so prepared, 

 we are not surprised to find that the ammonia is separated from the gas instantly 

 it comes in contact with it ; in fact, where we are passin" from 1 to_ 3 millions 

 feet of gas in 24 hours, we cannot detect any ammonia until the material is satu- 

 rated to within 1 or 2 inches of the siuiace. 



The material being very porous, oifers very little obstruction to the passage of 

 the gas, and so scarcely increases the pressure. 



All those who are engaged in the manufacture of sulphate of ammonia from the 

 ammoniacal liquor obtained from gas-works, well know the great loss of this salt 

 carried away by the steam, either in evaporating a solution to the crystallizing 

 poiut, or in passing the ammoniacal vapoui's through the acid. On the large scale 

 the loss is fi-oni 10 to 20 per cent. 



In the acid prepared as already stated, and converted into sulphate of ammonia, 

 at the temperature of the gas as it passes through the purifier there is no loss ; for 

 every equivalent of sulphmic acid used, an equivalent of sulphate of ammonia is 

 received. In an economical point of view this is a great saving ; but there is still 

 further economy in the labour, because the very process of removing the ammonia 

 from the gas converts it into sulphate of ammonia ready for the market. 



The material as discharged from the pmifier contains from 60 to 60 per cent, of 

 sulphate of ammonia applicable for manure pui-poses. 



The author claimed no novelty, either in the use of sulphuric acid alone or mixed 

 with sawdust, but thought its application as a free acid, when saturated with car- 

 bonaceous matter, might be of interest to the Section. 



On Madder PhotograjiJis. By John Meecee, F.B.S. 



On PJiotor/rapJiic Spectra of the Electric Light. 

 By Professor W. A. Miiler, M.D., F.E.S. 



The apparatus by which the spectra may be photographed consists of an ordinary 

 camera obscm-a attached to the end of a long wooden tube, which opens into a 

 cylindrical box, within which is a prism glass, or a hoUow prism filled with bisul- 

 phide of carbon. If the prism be so adjusted as to throw the solar rays, reflected 

 from a heliostat, upon the screen of a camera, and the wires which transmit the 

 sparks fi'om Ruhmkoi-lf's coil are placed in front of the imcovered portion of the 

 slit, the two spectra are simultaneously impressed. The solar beam is easily inter- 

 cepted at the proper time by means of a small screen, and the electric spectmm is al- 

 lowed to continue its action for two or three, or six minutes, as may be necessary. 

 The author did not find that anything was gained in distinctness by interposing a 

 lens of short focus between the slit and the wire which supplied the sparks, with 

 the view of rendering the rays of the electric light parallel like those of the sun, 

 owing to the absorbent action of the glass weakening the photographic effect ; and 

 the flickering motion of the sparks being magnified by the lens, rendered the lines 

 less distinct than when the lens was not used. Although with each of the metals 

 (including platinum, gold, silver, copper, zinc, aluminmn, magnesium, iron), when 

 the spark was taken in air, he obtained decided photographs, it appeared that in 

 each case the impressed spectrum was very nearly the same, proving that few of 



